The invention concerns dental implants.
A dental implant is the prosthetic equivalent of the root of a tooth. Despite appearances, the root of a tooth, with its very small volume, is endowed with astonishing properties. It must be able to withstand stresses of the order of ten to thirty kg per cm2, and its substance must be able to resist the mechanical stresses generated by mastication.
The root in fact serves to transmit the masticatory forces from the muscles to the crown of the tooth via the jaw bones. The contact between the bone seat and the root is thus of crucial importance. The problem is that a bone is not a homogeneous structure: beneath its very strong cortical walls extends its medullary zone, which is of spongy appearance and offers negligible mechanical support for an implant. It is therefore imperative that a dental implant passes through the medullary zone and anchors firmly in the cortical walls. Current dental implants thus require at least 8 to 15 mm of bone structure in order to be fitted in place. This fitting is done by screwing after a hole has been drilled in the upper or lower jaw bone.
However, this technique can only be used on patients who have a sufficient bone support, corresponding to classification SD 1 in implantology.
This classification is based on the height of the floor of the maxillary sinus in the technique of bicortical implants; SD1 corresponds to a floor height of greater than 10 mm.
According to the same classification, SD2 corresponds to a floor height of between 8 and 10 mm, SD3 to a floor height of between 5 and 8 mm, and SD4 to a floor height of between 0 and 5 mm (which requires filling).
In addition, after the implant support has been fitted in place, it is generally necessary to wait nearly five months before being able to place any load on the crown of the tooth.
EP 336,082 has disclosed a dental pin with a thread pitch used to fix a crown in the root of a tooth. Orifices are provided in the pin for the purpose of axial injection of a cement. However, such a technique cannot be applied to the jaw.
The alveolar bone has the role of supporting the teeth. When these disappear, the bone, which has lost its inherent function, is resorbed. The bone can also degrade for other reasons (various conditions, tumours, etc.).
For subjects corresponding to higher stages of deterioration (SD2, SD3 and SD4), the cortical parts of the bone support no longer provide a sufficient thickness for fitting an implant. In this case, a bone graft is performed in the maxillary sinus in order to increase the thickness of the bone support. The grafts used are slivers of bone taken from the patient himself. After ossification (which itself generally takes about 5 months), an implant can be fitted in place in accordance with the principles described above.
The object of the invention is to make it possible to treat stages SD2 or above without recourse to major treatment. Another object of the invention is to be able to permit immediate loading of the implanted tooth.
The subject of the invention is a dental implant for anchoring in a bone structure, comprising a head intended to support a dental prosthesis and a threaded root of cylindrical substance, in which the threaded root has an internal cavity and at least one lateral orifice connecting this internal cavity and the external lateral face of the root, the axial position of this orifice being such that when the implant is in position, this at least one orifice opens out on a medullary zone of the bone structure.
The dimensions of this at least one lateral orifice advantageously allow a hardenable material to be introduced into the internal cavity via a hollow needle.
The internal cavity can also have an axial orifice at its distal end.
This at least one lateral orifice preferably has an oval cross section, the main axis of this oval cross section extending in a plane perpendicular to the axis of the root.
The axial length is preferably between 3 and 8 mm.
According to an advantageous embodiment, the implant comprises a device for indicating the position of the lateral orifice, for example a removable tongue which can be attached to the head of the implant.
Another subject of the invention is a kit designed for fitting a dental implant in place, comprising:
an implant such as has been described above;
a biocompatible hardenable fluid;
a device for indicating the position of the lateral orifice of the implant;
a hollow needle injection device with which, when the implant is in place, it is possible to inject the biocompatible hardenable fluid through the bone and into the internal cavity of the implant;
optionally, a spatula which is retractable in a hollow needle; the hollow needle is preferably made of a shape-memory metal, capable of changing from an initial straight shape to a curved shape.
Another subject of the invention is a method for fixing a dental implant in a jaw bone, which method comprises the following operations:
drilling a hole in the jaw bone from its cortical wall as far as a medullary zone in such a way as to form an alveolus with the dimensions of an implant;
screwing into place an implant whose threaded root has an internal cavity, at least one lateral orifice connecting this internal cavity and the external lateral face of the root, the axial position of this orifice being such that when the implant is in position, this at least one orifice opens out on a medullary zone of the bone structure;
inserting a hollow needle through the jaw bone as far as the alveolus;
injecting a biocompatible hardenable fluid into the internal cavity of the implant;
distributing the hardenable fluid in the volume around the prosthesis, in the lateral orifices and in the internal cavity of the implant;
partially withdrawing the hollow needle;
distributing the hardenable fluid in the medullary zone of the jaw;
leaving the hardenable fluid to harden.
This method can additionally comprise the following operations:
inserting a hollow needle through the jaw bone to a point below the mucosa of the maxillary sinus, substantially level with the alveolus of the implant;
deploying a spatula via the hollow needle;
detaching the mucosa from the bone using the spatula;
retracting the spatula through the hollow needle;
injecting a biocompatible hardenable fluid between the bone and the mucosa.